Sunan an-Nasa'i
It was narrated that Al-Hasan and Muhammad said: "Combing one's hair (should be done) every other day."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا بِشْرٌ، عَنْ يُونُسَ، عَنِ الْحَسَنِ، وَمُحَمَّدٍ، قَالاَ التَّرَجُّلُ غِبٌّ .
Grade: Da'if (Darussalam)
Reference